Percutaneous Transluminal Angioplasty (PTA) is a medical procedure for widening a stenosis or constriction of a bodily passage. The most common application is to widen the passage of a blood vessel, such as an artery, which has been constricted by the build-up of cholesterol fats or atherosclerotic plaque. When this medical procedure is applied to a coronary artery, it is referred to as Percutaneous Transluminal Coronary Angioplasty (PTCA).
Typically, a tip mounted balloon of a balloon catheter is advanced over a guidewire to the stenosis. Once the balloon catheter is properly positioned, the balloon is inflated to compress the plaque against the vessel walls and widen the stenosis. Problems occur, however, when the dilatation of the occlusion forms fissures, flaps and/or dissections which may ultimately cause reclosure or restenosis of the vessel.
To maintain vessel patency and/or strengthen the area undergoing angioplasty or other treatment, an intravascular prosthesis may be employed. These devices are usually introduced percutaneously, transported transluminally and positioned at a desired location within the widened stenosis of the patient. One form of an intravascular prosthesis is a radially expandable stent device which is typically positioned at the tip of a balloon catheter and is implanted by expansion of the balloon when the balloon and stent device are at the desired location. Expansion of the balloon portion of the catheter can simultaneously compress plaque at that location and expand the stent to its proper implantation size. The balloon portion of the catheter is then deflated and withdrawn from the vessel, leaving the implanted stent as a permanent scaffold to reduce the chance of restenosis.
To adequately mount an unexpanded stent onto the balloon catheter for delivery into the patient, the stent is "crimped" or otherwise radially collapsed sufficiently to attach it to the balloon. One of the most favored crimping techniques is manual crimping performed by the physician in the catheter laboratory. This process enables the physician to "feel" the crimp to determine the crimp quality. The proper crimping of a stent about a balloon catheter, however, is a technique acquired only through practice and can be affected by a variety of subjective conditions. Too much or too little pressure may be applied and the balloon and/or stent may be damaged, lost, or may not otherwise perform as desired during the procedure. In contrast, the physician may not apply sufficient crimping pressure to the stent to load it onto the balloon. During advancement through the vessel or upon deployment, an insufficiently crimped stent may slip or rotate on the catheter during, or in the worst case scenario, come off the balloon catheter entirely; the result of which is not desirable. Moreover, when applying radioactive or radioisotope embedded stents, direct manual handling by physicians and laboratory technicians should be avoided. Such radioisotope embedded stents, for example, are those disclosed in U.S. Pat. Nos.: 5,059,166; 5,176,617; 5,840,009 and 5,871,437, each of which is incorporated by reference in their entirety.
In other instances, the stents may be pre-crimped or preattached onto their associated delivery balloon at the time of production by the manufacturer. While these devices more uniformly control crimping quality, a large inventory of stent-bearing angioplasty catheters must be maintained to accommodate the variety of stent types, diameters and stent lengths for each balloon catheter type. Thus, maintaining such an inventory is not only difficult to store, but can be very expensive as well.
Another technique commonly employed to crimp the stent onto the balloon catheter is through the use of a pair of modified plier-like tools which crimp down on the unexpanded stent. The performance of these tools, however, is not completely satisfactory since there is still a wide divergence between application force, profile and stent diameter. Problems arise when excessive crimping forces are applied to the crimp pliers which can damage the stent and/or balloon catheter. This is especially problemsome given the minute size of the stents which are typically on the order of about one (1) mm to four (4) mm in diameter before crimping. Non-uniformity of the crimping may also be experienced as well as the inability to determine when a reliable and uniform crimp has been achieved. Moreover, these designs are inadequate to handle radioactive or radioisotope embedded stents since they typically cause the physicians and/or laboratory technicians to be subjected to excessive radiation exposure.